Difference between divination and other methods? In the essential - what's basically happening - I don't think there is much difference. Those questions and possible answers Erin just described are very much the kind of thing you could do with an oracle, too. In either case, you're reaching out and connecting with a source of truth.
One difference is that with an oracle, you're entering into a system of some kind and it helps to learn about it. And better, more complete systems make it easier for the answer to get through to you - and the latest glossy card pack may or may not have what it takes. There's a case for saying that if you can make a direction connection with the same source that speaks through the oracle, why bother with the oracle at all? (That might be another thread!)
Another difference is that not everyone has the kind of gift Erin has to make the direct connection, reliably, skillfully and in full awareness. (Or maybe everyone has it in potential, but most of us have no clue how to access it... Erin, what do you think?) You don't need that kind of gift or self-belief to use an oracle. Though working with one, over the years, may develop your own native gifts of direct insight.
And using an oracle is a kind of insurance against human error. It's far from being perfect - people can interpret creatively if there's an answer they want badly enough... - but the I Ching in particular can make it very hard to kid yourself. The structure of the reading itself will sort out to some extent what elements of the situation are your own desires and fears. A reader working on her own has to sense this by herself - and may be picking up, telepathically/empathically, a lot of detail from the person she's reading for.
Hope that helps!